1. Field of the Invention
This invention relates to a stage apparatus, and more particularly, though not exclusively, to a stage apparatus that can be used in a semiconductor exposure apparatus and a machine tool.
2. Description of the Related Art
Conventionally, an apparatus called a stepper and an apparatus called a scanner have been known as parts of an exposure apparatus used for semiconductor devices. A stepper moves a semiconductor wafer on a stage apparatus in stepped movements under a projection lens so that a pattern image formed on a reticle can be projected in a smaller scale with an exposure light through a projection lens and sequentially exposed onto a plurality of exposure areas on the single wafer. Meanwhile, a scanner moves a wafer on a wafer stage and a reticle on a reticle stage relative to a projection lens and applies an exposure light in a slit shape during scanning movements so that a reticle pattern is projected onto the wafer.
These days, as semiconductor devices become increasingly miniaturized and highly integrated, higher positioning accuracy and higher speed for improved productivity are in demand for stage apparatuses.
FIGS. 8A and 8B are an exploded perspective view and an assembly drawing of a conventional stage apparatus.
Main components of a wafer stage include a coarse moving stage 90 that is provided with X coarse moving linear motors 91 and Y coarse moving linear motors 92 for moving a coarse moving slider 93 in the direction of the X and Y axes in long strokes and a fine moving stage 100 for precision positioning. The fine moving stage 100 is laid out on the coarse moving slider 93 through a coarse moving stage top panel 120, and a fine moving stage top panel 101 is controlled directly with the linear motors in six axial directions.
FIGS. 9A to 9C are an exploded perspective view of the fine moving stage top panel and an exploded perspective view and an assembly drawing of the fine moving stage shown in FIGS. 8A and 8B.
The fine moving stage top panel 101 has the outer shape of a rectangular plate, and is provided with a wafer chuck 102 for mounting a wafer in its center.
The fine moving stage top panel 101 has seven linear motors 106 to 112 installed on its bottom surface between the bottom surface and the coarse moving stage top panel 120. Among the seven linear motors, three linear motors 106 to 108, which are laid out on the peripheral edges of the fine moving stage top panel 101, form a Z linear motor that generates a thrust in the direction of the Z axis in the figure. The remaining four linear motors 109 to 112 are laid out in the approximate center of the fine moving stage top panel 101. Among these, two linear motors 109 and 110 form an X linear motor that generates a thrust in the direction of the X axis in the figure, and the remaining two linear motors 111 and 112 form a Y linear motor that generates a thrust in the direction of the Y axis.
By driving these linear motors in combination, a driving force can be generated without contact in the six axis directions, X, Y, Z, θx, θy, and θz.
In addition, the fine moving stage top panel 101 is provided with mirrors 103 to 105 on its sides for reflecting a laser of an interferometer so that the position of the wafer chuck 102 can be measured. More specifically, a total of six optical beams, not shown, are applied to the fine moving stage top panel 101 to measure in six degrees of freedom the position of the fine moving stage top panel 101. With two beams of the interferometer that are parallel to the X axis but are different in Z position, the position in the direction of the X axis and the amount of rotation in the θy direction are measured. With three beams of the interferometer that are parallel to the Y axis but are different in X position and in Z position, the position in the direction of the Y axis and the amount of rotation in the θx and θz directions are measured. Likewise, with a beam applied to a surface portion of the mirror (104), the position in the direction of the Z axis is measured. Although in fact the values measured with these beams are not independent but interfere with one another, by performing a coordinate transformation as a rigid body, X, Y, Z, θx, θy, and θz of a representative position can be measured.
The above-mentioned linear motors and measurement system make it possible to control the fine moving stage 100 to be a desired position in six degrees of freedom.
In addition, an electromagnetic actuator that applies an acceleration force to the fine moving stage according to acceleration and deceleration of the coarse moving stage is provided between the fine moving stage and the coarse moving stage so that an acceleration force is applied to the fine moving stage in the deceleration and acceleration section of the coarse moving stage.
The electromagnetic actuator comprises an I core 204 and an E-shaped electromagnet 206 (an E core 207 and a coil 208). A gap between the E core 207 and the I core 204 is as small as several tens of microns, and, generally speaking, compared to linear motors, a large force can be generated with a much smaller current. The thrust generated by the electromagnetic actuator is in the direction normal to the surface the E core facing the I core. Since the E-shaped electromagnet 206 can only generate an attraction, an electromagnet for generating an attraction on a positive (+) side and an electromagnet for generating an attraction on a negative (−) side are provided for each of the directions of the X and Y axes.
Furthermore, by making the I core 204 in an arc shape around the Z axis and by making the end face of the letter E of the E core 207 in an arc shape around the Z axis, the four I cores and the four E cores can freely rotate around the Z axis without contacting one another. This eliminates any change in the gapduring rotation, and therefore there is no change in the attraction generated by the electromagnet with the same current.
In addition, the I core 204 and the E core 207 are formed by layering thin plates while keeping the layers electrically isolated so that an eddy current is prevented from flowing within the yoke as magnetic flux changes occur. This makes it possible not only to control attractions up to high frequencies, but also to reduce heat generation caused by an eddy current.
Furthermore, by laying out a line of action of the force generated by the electromagnetic actuator at a location that approximately corresponds to the center of gravity in the direction of the Z axis and in the direction of the X or Y axis of the movable unit of the fine moving stage as a whole, application of an unnecessary rotation force to the fine moving stage is prevented. This eliminates the need for the linear motors to compensate for the unnecessary rotation force so as to make it possible to suppress heat generation of the motors.
As mentioned above, by having the electromagnetic actuator take charge of acceleration forces of the fine moving stage and generate acceleration forces in a precise manner, the heat generation can be suppressed of the linear motors and to suppress variation errors of the interferometer and deteriorations in stage positioning accuracy due to thermal expansion and other effects.
A coil spring 121 is provided between the fine moving stage and the coarse moving stage so that the weight of the wafer top panel 101 is supported. Thus, the Z fine moving linear motor described above does not need to generate a thrust for supporting the weight of the wafer top panel 101, and needs only to generate a small force for correcting a deviation from a target position. Refer to Japanese Patent Laid-Open No. 2003-022960 for an example.
One can use a stage apparatus to secure a stroke necessary for the apparatus, and to restrict excessive movement determined by constraints of the apparatus.
For example, for a stroke necessary for a fine moving stage in an exposure apparatus, there are minute rotations around the X and Y axes to allow exposure light to intersect at right angles with a wafer so that a normal pattern image is printed with respect to the shape of the wafer surface. In addition, there are other rotations including a minute rotation around the Z axis for correcting deviations in rotational position at the early stage when the wafer is fixed to the wafer chuck.
Meanwhile, as to the amounts of movement, an excessive amount of translational movement is conceivable. In examples shown in FIGS. 8A, 8B, and 9A to 9C, the gap between the fine moving stage and the coarse moving stage is the gap between the E core 207 and the I core 204 of the electromagnetic actuator, which represents the smallest gap, and is as small as several tens of microns. Because of this, in an assembly stage and in a preparation stage for controls such as debugging, and during adjustment, it can be difficult to maintain the gap between the I core 204 and the E core 207, and they may contact each other. In case of such a contact, the I core 204 and the E core 207 may incur an indentation or wear. This may cause a local change in the gap between the I core 204 and the E core 207, making it difficult to generate an accurate acceleration force, which can deteriorate positioning accuracy.
In addition, the stage apparatus can become uncontrollable due to the effects incurred from unexpected disturbance and the stage apparatus, in a precisely controlled state, instantly goes into a servo off state due to an emergency stop. Thus, the I core 204 and the E core 207 of the electromagnetic actuator, which correspond to the smallest gap between the coarse moving stage and the fine moving stage, can collide with each other and cause the electromagnetic actuator to break. It is thus necessary to prevent damage or breakage of the actuator to achieve stable driving of the stage apparatus.
Since both an exposure apparatus and a stage apparatus are generally provided with many components such as refrigerant piping for cooling, electric cable and sensor, excessive amounts of translational and rotational movement which can damage the components, also becomes a problem. In particular, in a wafer stage, it can be necessary to relatively move an unshown three-pin for wafer replacement in a stroke in the direction of the z axis relative to the fine moving stage, and when the three-pin is fixed, the fine moving stage can be moved in a stroke in the direction of the Z axis in the order of several millimeters. Thus, it is useful to secure a stroke in the direction of the Z axis and to suppress excessive amounts of translational and rotational movement in the direction of the other axes.